A brushless motor needs switching elements for turning on or off electric power to be supplied to coils of the stator. Because the switching elements generate heat much, it is necessary to let the heat out.
In an example of a structure of a brushless motor for transferring the heat generated in the switching elements, a base of a circuit board provided in the brushless motor is made of a metal, and the base is fixed to stator iron cores (for example, Japanese Patent laid open Publication 4-161037/1992). The heat generated in the switching elements is conducted to the base of the circuit board and further to the stator iron cores. The stator iron cores have a function similar to radiation fins, and the heat is radiated effectively through the stator iron cores.
However, because the heat generated in the base conducts through the metallic base of the circuit board, the temperature of the circuit board becomes higher. Therefore, it is a problem that components other than the switching elements mounted on the circuit board are affected by the heat.